Recent research efforts have focused on treating patients suffering from cognitive deficits with agonists that may activate muscarinic cholinergic receptors. Molecular biological studies have identified and characterized five subtypes of muscarinic receptors (M1, M2 . . . M5), each with a unique amino acid sequence, tissue-specific expression, ligand binding profile and associated biochemical response. The use of muscarinic receptor agonists for treating cognitive defects, however, may be hindered by the undesirable cholinergic side effects produced by their administration, including diaphoresis (excessive sweating), hypersalivation (excessive salivation), flushing (reddening of the skin, especially in the cheeks and neck), gastro-intestinal tract upsets, such as increased stomach acid, nausea, vomiting and diarrhea, breathing difficulties, tachycardia (slow heart beat), dizziness, syncope (fainting), headache, convulsions, and somnolence (sleepiness).